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<HTML LANG="en-us"
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>14.1 Cons Concepts | Common Lisp Nova Spec</TITLE
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><H2 ID="sec_14_1" CLASS="HeadII"
>14.1 Cons Concepts</H2
><UL CLASS="subtoc"
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_1"
>14.1.1 Conses as Trees</A
></LI
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_1_1"
>14.1.1.1 General Restrictions on Parameters that must be Trees</A
></LI
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_2"
>14.1.2 Conses as Lists</A
></LI
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_2_1"
>14.1.2.1 Lists as Association Lists</A
></LI
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_2_2"
>14.1.2.2 Lists as Sets</A
></LI
><LI
><A HREF="14_1_Cons_Concepts.html#sec_14_1_2_3"
>14.1.2.3 General Restrictions on Parameters that must be Lists</A
></LI
></UL
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>cons</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="cons"
></SPAN
>is a compound data <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>object</EM
></A
> having two components called the <A HREF="26_1_Glossary.html#car"
><EM CLASS="term"
>car</EM
></A
> and the <A HREF="26_1_Glossary.html#cdr"
><EM CLASS="term"
>cdr</EM
></A
>.</P
><DIV CLASS="displaythree"
><FIGURE CLASS="boxfig"
><DIV CLASS="figbody"
><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0" WIDTH="100%"
><TBODY
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE=";padding-right:1em"
><A HREF="f_car.html" CLASS="misc"
><B
>car</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE="padding-left:1em;padding-right:1em"
> <A HREF="f_cons.html" CLASS="funref"
><B
>cons</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE="padding-left:1em;"
> <A HREF="f_rplaca.html" CLASS="misc"
><B
>rplacd</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE=";padding-right:1em"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE="padding-left:1em;padding-right:1em"
> <A HREF="f_rplaca.html" CLASS="misc"
><B
>rplaca</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" NOWRAP="NOWRAP" STYLE="padding-left:1em;"
><SPAN CLASS="misc"
></SPAN
></TD
></TR
></TBODY
></TABLE
></DIV
><FIGCAPTION CLASS="caption"
><B
>Figure 14&#8211;1. Some defined names relating to conses.</B
></FIGCAPTION
></FIGURE
></DIV
><P CLASS="j"
>Depending on context, a group of connected <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> can be viewed in a variety of different ways. A variety of operations is provided to support each of these various views.</P
><H3 ID="sec_14_1_1" CLASS="HeadIII"
>14.1.1 Conses as Trees</H3
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>tree</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="tree"
></SPAN
>is a binary recursive data structure made up of <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> and <A HREF="26_1_Glossary.html#atom"
><EM CLASS="term"
>atoms</EM
></A
>: the <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> are themselves also <A HREF="26_1_Glossary.html#tree"
><EM CLASS="term"
>trees</EM
></A
> (sometimes called &#8220;subtrees&#8221; or &#8220;branches&#8221;), and the <A HREF="26_1_Glossary.html#atom"
><EM CLASS="term"
>atoms</EM
></A
> are terminal nodes (sometimes called <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>leaves</SPAN
></DFN
><SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="leaves"
></SPAN
>). Typically, the <EM CLASS="term"
>leaves</EM
> represent data while the branches establish some relationship among that data.</P
><FIGURE CLASS="boxfig"
><DIV CLASS="figbody"
><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0" WIDTH="100%"
><TBODY
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
><A HREF="f_car.html" CLASS="misc"
><B
>caaaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caddar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>nsubst</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caaadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cadddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cddaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>nsubst-if</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cddadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>nsubst-if-not</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caadar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cddar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_nthcdr.html" CLASS="misc"
><B
>nthcdr</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caaddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdaaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdddar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_sublis.html" CLASS="misc"
><B
>sublis</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdaadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cddddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>subst</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>caar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>subst-if</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cadaar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdadar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_subst.html" CLASS="misc"
><B
>subst-if-not</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cadadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdaddr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_copy-tree.html" CLASS="misc"
><B
>copy-tree</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_tree-equal.html" CLASS="misc"
><B
>tree-equal</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cadar</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_car.html" CLASS="misc"
><B
>cdadr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_sublis.html" CLASS="misc"
><B
>nsublis</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
><SPAN CLASS="misc"
></SPAN
></TD
></TR
></TBODY
></TABLE
></DIV
><FIGCAPTION CLASS="caption"
><B
>Figure 14&#8211;2. Some defined names relating to trees.</B
></FIGCAPTION
></FIGURE
><H4 ID="sec_14_1_1_1" CLASS="HeadIV"
>14.1.1.1 General Restrictions on Parameters that must be Trees</H4
><P CLASS="j"
>Except as explicitly stated otherwise, for any <A HREF="26_1_Glossary.html#standardized"
><EM CLASS="term"
>standardized</EM
></A
> <A HREF="26_1_Glossary.html#function"
><EM CLASS="term"
>function</EM
></A
> that takes a <A HREF="26_1_Glossary.html#parameter"
><EM CLASS="term"
>parameter</EM
></A
> that is required to be a <A HREF="26_1_Glossary.html#tree"
><EM CLASS="term"
>tree</EM
></A
>, the consequences are undefined if that <A HREF="26_1_Glossary.html#tree"
><EM CLASS="term"
>tree</EM
></A
> is circular.</P
><H3 ID="sec_14_1_2" CLASS="HeadIII"
>14.1.2 Conses as Lists</H3
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="list"
></SPAN
>is a chain of <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> in which the <A HREF="26_1_Glossary.html#car"
><EM CLASS="term"
>car</EM
></A
> of each <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
> is an <A HREF="26_1_Glossary.html#element"
><EM CLASS="term"
>element</EM
></A
> of the <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
>, and the <A HREF="26_1_Glossary.html#cdr"
><EM CLASS="term"
>cdr</EM
></A
> of each <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
> is either the next link in the chain or a terminating <A HREF="26_1_Glossary.html#atom"
><EM CLASS="term"
>atom</EM
></A
>. </P
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>proper</SPAN
> <SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="proper list"
></SPAN
>is a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> terminated by the <A HREF="26_1_Glossary.html#empty_list"
><EM CLASS="term"
>empty list</EM
></A
>. The <A HREF="26_1_Glossary.html#empty_list"
><EM CLASS="term"
>empty list</EM
></A
> is a <A HREF="26_1_Glossary.html#proper_list"
><EM CLASS="term"
>proper list</EM
></A
>, but is not a <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
>. </P
><P CLASS="j"
>An <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>improper</SPAN
> <SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="improper list"
></SPAN
>is a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> that is not a <A HREF="26_1_Glossary.html#proper_list"
><EM CLASS="term"
>proper list</EM
></A
>; that is, it is a <A HREF="26_1_Glossary.html#circular_list"
><EM CLASS="term"
>circular list</EM
></A
> or a <A HREF="26_1_Glossary.html#dotted_list"
><EM CLASS="term"
>dotted list</EM
></A
>. </P
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>dotted</SPAN
> <SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="dotted list"
></SPAN
>is a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> that has a terminating <A HREF="26_1_Glossary.html#atom"
><EM CLASS="term"
>atom</EM
></A
> that is not the <A HREF="26_1_Glossary.html#empty_list"
><EM CLASS="term"
>empty list</EM
></A
>. A <A HREF="26_1_Glossary.html#non-nil"
><EM CLASS="term"
>non-nil</EM
></A
> <A HREF="26_1_Glossary.html#atom"
><EM CLASS="term"
>atom</EM
></A
> by itself is not considered to be a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> of any kind &#8212; not even a <A HREF="26_1_Glossary.html#dotted_list"
><EM CLASS="term"
>dotted list</EM
></A
>. </P
><P CLASS="j"
>A <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>circular</SPAN
> <SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="circular list"
></SPAN
>is a chain of <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> that has no termination because some <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
> in the chain is the <A HREF="26_1_Glossary.html#cdr"
><EM CLASS="term"
>cdr</EM
></A
> of a later <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
>.</P
><FIGURE CLASS="boxfig"
><DIV CLASS="figbody"
><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0" WIDTH="100%"
><TBODY
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
><A HREF="f_append.html" CLASS="misc"
><B
>append</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_last.html" CLASS="misc"
><B
>last</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_butlast.html" CLASS="misc"
><B
>nbutlast</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_rest.html" CLASS="misc"
><B
>rest</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_butlast.html" CLASS="misc"
><B
>butlast</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_ldiff.html" CLASS="misc"
><B
>ldiff</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_nconc.html" CLASS="misc"
><B
>nconc</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_revappend.html" CLASS="misc"
><B
>revappend</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_copy-alist.html" CLASS="misc"
><B
>copy-alist</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <SPAN CLASS="misc"
><B
>list</B
></SPAN
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_first.html" CLASS="misc"
><B
>ninth</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_first.html" CLASS="misc"
><B
>second</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_copy-list.html" CLASS="misc"
><B
>copy-list</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_list.html" CLASS="misc"
><B
>list*</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_revappend.html" CLASS="misc"
><B
>nreconc</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_first.html" CLASS="misc"
><B
>seventh</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_first.html" CLASS="misc"
><B
>eighth</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_list-length.html" CLASS="misc"
><B
>list-length</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_nth.html" CLASS="misc"
><B
>nth</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_first.html" CLASS="misc"
><B
>sixth</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_endp.html" CLASS="misc"
><B
>endp</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_make-list.html" CLASS="misc"
><B
>make-list</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_nthcdr.html" CLASS="misc"
><B
>nthcdr</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_ldiff.html" CLASS="misc"
><B
>tailp</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_first.html" CLASS="misc"
><B
>fifth</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <SPAN CLASS="misc"
><B
>member</B
></SPAN
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_pop.html" CLASS="misc"
><B
>pop</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_first.html" CLASS="misc"
><B
>tenth</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_first.html" CLASS="misc"
><B
>first</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_member.html" CLASS="misc"
><B
>member-if</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_push.html" CLASS="misc"
><B
>push</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_first.html" CLASS="misc"
><B
>third</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_first.html" CLASS="misc"
><B
>fourth</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_member.html" CLASS="misc"
><B
>member-if-not</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_pushnew.html" CLASS="misc"
><B
>pushnew</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
><SPAN CLASS="misc"
></SPAN
></TD
></TR
></TBODY
></TABLE
></DIV
><FIGCAPTION CLASS="caption"
><B
>Figure 14&#8211;3. Some defined names relating to lists.</B
></FIGCAPTION
></FIGURE
><H4 ID="sec_14_1_2_1" CLASS="HeadIV"
>14.1.2.1 Lists as Association Lists</H4
><P CLASS="j"
>An <DFN CLASS="newterm"
><SPAN CLASS="cmbxsl"
>association</SPAN
> <SPAN CLASS="cmbxsl"
>list</SPAN
></DFN
> <SPAN CLASS="idx" DATA-KIND="idxterm" DATA-TERM="association list"
></SPAN
>is a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> of <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>conses</EM
></A
> representing an association of <A HREF="26_1_Glossary.html#key"
><EM CLASS="term"
>keys</EM
></A
> with <A HREF="26_1_Glossary.html#value"
><EM CLASS="term"
>values</EM
></A
>, where the <A HREF="26_1_Glossary.html#car"
><EM CLASS="term"
>car</EM
></A
> of each <A HREF="26_1_Glossary.html#cons"
><EM CLASS="term"
>cons</EM
></A
> is the <A HREF="26_1_Glossary.html#key"
><EM CLASS="term"
>key</EM
></A
> and the <A HREF="26_1_Glossary.html#cdr"
><EM CLASS="term"
>cdr</EM
></A
> is the <A HREF="26_1_Glossary.html#value"
><EM CLASS="term"
>value</EM
></A
> associated with that <A HREF="26_1_Glossary.html#key"
><EM CLASS="term"
>key</EM
></A
>.</P
><FIGURE CLASS="boxfig"
><DIV CLASS="figbody"
><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0" WIDTH="100%"
><TBODY
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
><A HREF="f_acons.html" CLASS="misc"
><B
>acons</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_assoc.html" CLASS="misc"
><B
>assoc-if</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_pairlis.html" CLASS="misc"
><B
>pairlis</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_rassoc.html" CLASS="misc"
><B
>rassoc-if</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_assoc.html" CLASS="misc"
><B
>assoc</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_assoc.html" CLASS="misc"
><B
>assoc-if-not</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_rassoc.html" CLASS="misc"
><B
>rassoc</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_rassoc.html" CLASS="misc"
><B
>rassoc-if-not</B
></A
></TD
></TR
></TBODY
></TABLE
></DIV
><FIGCAPTION CLASS="caption"
><B
>Figure 14&#8211;4. Some defined names related to assocation lists.</B
></FIGCAPTION
></FIGURE
><H4 ID="sec_14_1_2_2" CLASS="HeadIV"
>14.1.2.2 Lists as Sets</H4
><P CLASS="j"
><A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>Lists</EM
></A
> are sometimes viewed as sets by considering their elements unordered and by assuming there is no duplication of elements.</P
><FIGURE CLASS="boxfig"
><DIV CLASS="figbody"
><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0" WIDTH="100%"
><TBODY
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
><A HREF="f_adjoin.html" CLASS="misc"
><B
>adjoin</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_set-difference.html" CLASS="misc"
><B
>nset-difference</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_set-difference.html" CLASS="misc"
><B
>set-difference</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
> <A HREF="f_union.html" CLASS="misc"
><B
>union</B
></A
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_intersection.html" CLASS="misc"
><B
>intersection</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_set-exclusive-or.html" CLASS="misc"
><B
>nset-exclusive-or</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_set-exclusive-or.html" CLASS="misc"
><B
>set-exclusive-or</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
><SPAN CLASS="misc"
></SPAN
></TD
></TR
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
> <A HREF="f_intersection.html" CLASS="misc"
><B
>nintersection</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_union.html" CLASS="misc"
><B
>nunion</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
> <A HREF="f_subsetp.html" CLASS="misc"
><B
>subsetp</B
></A
></TD
><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
><SPAN CLASS="misc"
></SPAN
></TD
></TR
></TBODY
></TABLE
></DIV
><FIGCAPTION CLASS="caption"
><B
>Figure 14&#8211;5. Some defined names related to sets.</B
></FIGCAPTION
></FIGURE
><H4 ID="sec_14_1_2_3" CLASS="HeadIV"
>14.1.2.3 General Restrictions on Parameters that must be Lists</H4
><P CLASS="j"
>Except as explicitly specified otherwise, any <A HREF="26_1_Glossary.html#standardized"
><EM CLASS="term"
>standardized</EM
></A
> <A HREF="26_1_Glossary.html#function"
><EM CLASS="term"
>function</EM
></A
> that takes a <A HREF="26_1_Glossary.html#parameter"
><EM CLASS="term"
>parameter</EM
></A
> that is required to be a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> should be prepared to signal an error of <A HREF="26_1_Glossary.html#type"
><EM CLASS="term"
>type</EM
></A
> <A HREF="t_type-error.html" CLASS="typeref"
><B
>type-error</B
></A
> if the <A HREF="26_1_Glossary.html#value"
><EM CLASS="term"
>value</EM
></A
> received is a <A HREF="26_1_Glossary.html#dotted_list"
><EM CLASS="term"
>dotted list</EM
></A
>. </P
><P CLASS="j"
>Except as explicitly specified otherwise, for any <A HREF="26_1_Glossary.html#standardized"
><EM CLASS="term"
>standardized</EM
></A
> <A HREF="26_1_Glossary.html#function"
><EM CLASS="term"
>function</EM
></A
> that takes a <A HREF="26_1_Glossary.html#parameter"
><EM CLASS="term"
>parameter</EM
></A
> that is required to be a <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
>, the consequences are undefined if that <A HREF="26_1_Glossary.html#list"
><EM CLASS="term"
>list</EM
></A
> is <A HREF="26_1_Glossary.html#circular"
><EM CLASS="term"
>circular</EM
></A
>.</P
></SECTION
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